Spiffy Hacks

I cannot remember how the ebook reader works on the 3S.
I have some epub books and I have Calibre which can convert to lots of formats.
I just seem to be drawing a blank when trying to remember or find out how to get them on the 3s.
I seem to remember something about it, meh, not any more.

Thanks,

I believe the books on the tablets are simply done in flash.